A brief description is now given of a 3rd generation partnership project long term evolution (3GPP LTE, hereinafter simply referred to as LTE) communication system as an example of a mobile communication system to which the present invention is applicable.
FIG. 1 is a view schematically illustrating the network structure of an evolved universal mobile telecommunications system (E-UMTS) as an exemplary wireless communication system. The E-UMTS is an advanced version of a legacy universal mobile telecommunications system (UMTS) and basic standardization thereof is currently underway in 3GPP. E-UMTS may be generally referred to as an LTE system. For details of the technical specifications of UMTS and E-UMTS, reference may be made to Release 7 and Release 8 of “3rd Generation Partnership Project; Technical Specification Group Radio Access Network”.
Referring to FIG. 1, the E-UMTS includes a user equipment (UE), evolved Node Bs (eNode Bs or eNBs), and an access gateway (AG) which is located at an end of an evolved UMTS terrestrial radio access network (E-UTRAN) and connected to an external network. The eNBs may simultaneously transmit multiple data streams for a broadcast service, a multicast service, and/or a unicast service.
One or more cells are present per eNB. A cell is configured to use one of bandwidths of 1.44, 3, 5, 10, 15, and 20 MHz to provide a downlink or uplink transmission service to multiple UEs. Different cells may be configured to provide different bandwidths. The eNB controls data transmission and reception to and from a plurality of UEs. Regarding downlink (DL) data, the eNB transmits downlink scheduling information to notify a corresponding UE of a time/frequency domain in which data is to be transmitted, coding, data size, hybrid automatic repeat and request (HARQ)-related information, etc. by transmitting downlink scheduling information to the UE. In addition, regarding uplink (UL) data, the eNB transmits uplink scheduling information to a corresponding UE to inform the UE of an available time/frequency domain, coding, data size, HARQ-related information, etc. An interface for transmitting user traffic or control traffic may be used between eNBs. A core network (CN) may include the AG and a network node for user registration of the UE. The AG manages mobility of a UE on a tracking area (TA) basis, each TA including a plurality of cells.
Although wireless communication technology has been developed up to LTE based on wideband code division multiple access (WCDMA), demands and expectations of users and service providers continue to increase. In addition, since other radio access technologies continue to be developed, new advances in technology are required to secure future competitiveness. For example, reduction in costs per bit, increase in service availability, flexible use of frequency band, simple and open interface, appropriate power consumption of a UE, etc. are required.